The invention relates generally to inspection systems and more specifically to a method and system for inspection using eddy current (EC) probes.
Eddy currents are generally useful for providing a measurable parameter indicative of flaws in the surface and sub-surface of component. Eddy currents are typically affected by changes in the material properties such as electrical conductivity, magnetic permeability, presence of discontinuity, etc. Flaws in the component, such as microscopic hair-line cracks or pits, affect the localized resistance of the material. Flaws in a component usually cause localized variations in the eddy currents in the material. Accordingly, a component can be inspected for flaws by inducing eddy currents in the component and measuring the changes on the eddy currents.
Eddy current probes detect flaws in a component by sensing perturbations in eddy currents. These probes typically have coils operated at high frequency alternating currents that produce an alternating magnetic field into the component being inspected. The magnetic field induces eddy currents in the component. The strength of the eddy currents depends on the local resistivity of the component, which is affected by the presence of flaws in the component. These eddy currents create a magnetic field that varies in intensity with the distribution of the eddy currents on the component.
The magnetic field created by the eddy currents induces a voltage in a sense coil. The voltage is displayed as a signal which represents the material property of the component.
Inspection of engineering components and structures frequently utilize long probe holders with miniature differential eddy current probes. One advantage of using differential probes is the reduced sensitivity to the edge, when oriented symmetric to the edge. However, in practice, one does not always encounter a perfectly straight edge. In addition, small probe misalignments may also exist due to the probe fixtures.
Such conditions result in significant edge signals and hence a lower inspection reliability. Currently, edge signals are suppressed using a variety of techniques such as butting with additional material to provide a continuous inspection surface, using auxiliary probes and ferrite shields to focus the electromagnetic field, post-processing with image processing techniques to eliminate the edge signals. Such techniques, however, provide an incremental improvement in the elimination of the edge signal.
Thus, there is a need for a method and system that provides improved suppression of edge signals and detection of edge flaws in various components.